1. Field of the Invention
The present invents relates to a thinner composition for washing a photoresist in a process for manufacturing semiconductors. More specifically, the present invention relates to a thinner solvent composition for washing a photoresist in a process for manufacturing semiconductors, which can be used to remove the unnecessary or excess photoresist on the edge portion and the backside of the wafer, for the photoresist layer used as a mask.
2. Description of the Related Art
Among the stages in the process for manufacturing semiconductor devices, photolithography is one of the most important. The photolithography stage generally comprises coating a photoresist on a wafer, optically transferring the previously designed pattern, and properly etching the wafer according to the transferred pattern.
More specifically, the photolithography stage can be largely divided into the following steps:
1) a coating step where the photoresist is uniformly coated on the surface of the wafer; PA1 2) a soft baking step where the solvent is evaporated from the coated photoresist to intimately attach the photoresist to the surface of the wafer; PA1 3) a light-exposure step where the wafer is exposed to light, which is reductively projecting the circuit pattern on the mask repeatedly and sequentially by the use of a light source such as ultra-violet, to thereby transfer the circuit pattern onto the wafer; PA1 4) a developing step where selected portions of the photoresist, having different physical properties such as solubility caused by light sensitivity from the light-exposure step, are removed; PA1 5) a hard baking step for further adhering the photoresist, which remained on the wafer after the developing step, to the wafer; PA1 6) an etching step where predetermined portions of the wafers are etched in order to impart electric properties depending on the pattern developed on the wafer; PA1 7) a peeling step where the unneeded photoresist is removed.
In addition, the photolithography process requires another step where the excess photoresist coated on the edge or backside of the wafer is removed, after the soft baking step (2). Otherwise, if the photoresist remains on the edge or backside of the wafer, a variety of defects may occur in subsequent semiconductor processing steps, such as etching or ion injection, so that the overall yield of the semiconductor devices may be lowered.
According to the conventional art, in order to remove the photoresist existing on the edge or backside of the wafer, spraying nozzles are provided on the top and bottom of the wafer edge portion so that a thinner organic solvent composition is sprayed on the edge or backside of the wafer through the nozzles.
The present invention relates to an improved thinner solvent composition. The elements which determine the performance of the thinner include solubility rate, volatility and viscosity.
The solubility rate of a thinner determines how effectively the thinner can dissolve and remove the photoresist. It is obvious that the desired solubility rate depends on the object of using the thinner.
As to volatility, the thinner should be easily evaporated after removing the photoresist so that the thinner does not remain on the surface of the wafer. If a low volatility thinner remains on the surface of the wafer, the thinner itself would act as a polluting source in various processes, particularly the etching process, thereby lowering the yield of the semiconductor device. However, if the volatility is too high, the thinner would evaporate during handling causing contamination problems in the clean room.
The proper viscosity is also an essential property to facilitate the spraying of thinner through the nozzles. If the viscosity is too high, an excessively high spraying pressure would be required to spray the thinner through the nozzles. If viscosity is too low, the spray focus would deteriorate because the thinner could not be concentrated or focused on the contact position of the wafer after exiting the spray nozzles.
Particularly, in the case of edge rinsing, the thinner must have the proper solubility rate in order to ensure a smooth wafer cross section after treatment. As shown in FIGS. 1 and 2, if the solubility rate is too low, a so-called tailing condition occurs. This flow of partially solubilized photoresist or tail 3, occurs while rinsing the photoresist 2 that had been coated on the wafer 1.
On the other hand, as shown in FIGS. 3 through 5, if the solubility rate is too high, an erosion portion 4 of the photoresist 2, a so-called photoresist attack, may occur while rinsing the photoresist 2 which had been coated on the wafer 1. Both tailing and photoresist attack directly cause wafer inferiorities, thereby lowering the yield of the semiconductor devices.
If the volatility is too low, the thinner may remain at the edge portion of the wafers, particularly at the flat zone used in the alignment of the wafers after spin drying. Then, the remaining thinner would build-up again on the photoresist of the wafers after the developing step to make a lump of the photoresist at the flat zone portion, directly causing a lowering of the yield of semiconductor devices from the wafers. On the other hand, if the volatility is too high, the thinner would evaporate before completely removing the photoresist so that the cleaning efficiency of the photoresist would be lowered.
Conventional thinners, such as ethyleneglycol monoethylether acetate (ECA), n-butyl acetate (n-BA), propyleneglycol monomethylether acetate (PGMEA) and ethyl lactate (EL), or the like, have been used.
In the case of ethyleneglycol monoethylether acetate and n-butyl acetate, although the solubility rate is good, the volatility and inflammability are too high and they are toxic to humans when inhaled or contacted on the skin. In particular, the toxicity of ethyleneglycol monoethylether acetate may cause leukopenia and miscarriage of an embryo.
The solubility rate is too low to give a sufficient rinse effect in the case of propyleneglycol monomethylether acetate or ethyl lactate.
A rinse treating method using a rinse solvent comprising an ether compound represented by the general formula of R.sup.1 --O--(--CHR.sup.2 --CH.sub.2 --O--).sub.n --H has been disclosed in Korean Patent Publication No. 90-5345, which is incorporated herein by reference. According to the Publication, the rinse solvent has no toxicity. The rinse solvent may be used to remove and peel off the photoresist layer by completely depositing the wafer on which the photoresist had been coated in the solvent. However, the rinse solvent may not be used to remove (i.e., partially remove the photoresist from the edge and backside portions of the wafer) the photoresist by spraying the solvent through the nozzles.
Accordingly, there exists a need for a thinner having the proper solubility rate for certain photoresists, with proper volatility and viscosity, but without being toxic to humans.